Cellphone signals get personal to save power

作者：胡母修摁 发布时间：2019-03-07 04:14:02

By Paul Marks A cellphone base station antenna that follows each phone user with a dedicated radio “beam”, rather than broadcasting in many directions at once, could slash the energy used by the mobile communications industry. If it was taken up globally, the equivalent of five 1-gigawatt power stations could be switched off. So say engineers working for Green Touch, an international industrial and academic consortium set up to cut the energy used by the industry. An overwhelming 75 per cent of that energy is expended beaming phone calls, text messages and 3G internet signals into empty air. In a standard GSM/3G cellphone base station, three panel antennas facing 120 degrees apart cover all the users in a cell – up to around 60 calls per company at peak demand. But this means a lot of radio energy is radiated in directions where there are no users. So Green Touch members Huawei of China, Samsung of South Korea, Freescale Semiconductor of the US and Alcatel Lucent of France have cut these three antennas down into 16 slimmer ones, each addressing a 22.5-degree sector. By altering the timing, or phase, of the signals sent to just two of these panels, they can form a beam and steer it where they want it – effectively following a user. Using different frequencies, a pair of beam-forming antennas can follow several users at once, so little energy is wasted. In field experiments, Green Touch found that on average a 16-panel base station used just 6 per cent of the power used by three-panel set-up hosting the same number of calls. And when they doubled the number of panels to 32, the saving doubled too. “The total power drops by a factor of 16 – and it continues to scale: every time we double the number of elements we halve the radiated power,” says Greg Wright of Alcatel Lucent’s lab in Crawford Hill, New Jersey. “Focussing a beam on the user, rather than spreading the radio signal over the landscape, means we can greatly reduce the amount of power we need,” he says. The Green Touch team say the technology saves roughly 1 kilowatt per base station. If it was used to replace all the world’s existing base stations, it could save the power output of five power stations – five gigawatts. However, they have yet to develop the software that, for instance, allows one of their smart beam-forming cells to hand a mobile user from one cell to the next without dropping a call. “We don’t know the software overhead for this yet,” says Wright. “But we have demonstrated an important principle – that continuing to add antennas gives proportional reductions in power.” Green Touch chairman Gee Rittenhouse says the consortium’s role is to demonstrate power-saving technologies – not develop them for the market. “Commercialisation is really to be taken up outside of Green Touch,” he says. They will have their work cut out getting the idea adopted: cellphone network companies have proven resistant to energy-saving schemes. Tim Fowler, a wireless broadband engineer at Cambridge Consultants in the UK, says one confounding factor for the technology may be that it causes handsets to use more power while switching from one base station to the next. “This technology will inherently end up with a lot more signal handovers with their smaller antenna sectors – since users will be moving through sectors faster. So will handling those handovers eat battery power in the handset? That’s the kind of data they need to publish,” he says. More on these topics: